1. Field of Invention
This invention relates to and has among its objects the the provision of novel organic compounds and the use thereof in insect control, particularly inhibition of the growth of mosquito larvae. Further objects of the invention will be evident from the following description wherein parts and percentages are by weight unless otherwise specified. The symbol .phi. is used herein to represent the phenyl ##STR2## group.
2. Description of the Prior Art
One means for biological control of insect populations involves the use of compounds which inhibit the growth of insect larvae. Such compounds are referred to in the art as insect growth regulators or juvenile hormone mimics. Juvenile hormones are essential for growth and development of young larvae. The last instar larvae are equipped with internal physiological mechanisms which interrupt the secretion of these juvenile hormones resulting in a replacement of larval growth by pupal and adult growth--a process generally known as metamorphosis. Provision of an exogenous supply of a juvenile hormone or hormone analog at a critical period in larval development causes partial or complete inhibition of metamosphosis. Juvenile hormone mimics do not kill the larvae, but rather prevent the growth thereof beyond the larval or pupal stage. Consequently, the number of adults is substantially reduced. The juvenile hormone mimics actually cause several different situations, all of which result in controlling insect population. First of all, most of the treated larvae do not reach adulthood. Thus, the larvae survive for a period of time (possibly an entire growing season) as either larvae or pupae, and then die. During that period the larvae are, of course, very susceptible to predation and injurious climatic conditions. Furthermore, they are themselves incapable of reproduction, thus reducing the insect population for the next growing season. Secondly, some of the treated larvae may develop to various stages of adulthood. For example, the adult insect my only partially eclose, i.e., emerge from the larval or pupal shell. On the other hand, full eclosion may occur but the adult insect is either malformed or dead. In either case, the population of adult insects is substantially reduced.
The growth-inhibiting compounds have many advantages over insecticides and the like. First, the growth-inhibitors do not yield unwanted ecological side effects. Secondly, since the growth inhibitors act as juvenile hormone mimics, the insects do not develop a tolerance to the compounds. Thus, the compounds will not eventually become ineffective. Third, the growth-inhibiting compounds are not harmful to beneficial insects or mammals because they are quite specific for a particular kind of insect.
Polybutylorthobenzyl and parabenzyl phenols have been disclosed as larvae growth-inhibiting compounds. Mosquito News, Volume 31, No. 4, pp 513-516 (1971) and Chemical Abstracts, Volume 80, No. 768 h (1974) disclose compounds to control mosquitos having the structure ##STR3## wherein R is independently hydrogen or methyl.
Hanauye et al (U.S. Pat. No. 3,920,846) and Hanaue (German Offen. 2,425,713) disclose compounds having juvenile hormone activity effective in combatting mosquito larvae having the general formula ##STR4## wherein R is hydrogen or t-butyl, with the proviso that the hydroxyl group is in the ortho position with respect to R and at least one t-butyl group is present in the ortho position with respect to the hydroxyl group.
Ludvik (U.S. Pat. No. 3,839,586) teaches the method of preventing mosquito larvae from developing into adult stage by exposing the larvae to compounds of the structure ##STR5## wherein R is hydrogen, isopropylphenyl, alkyl of from 1 to 6 carbons, alkoxy of from 1 to 6 carbons and thioalkyl of from 1 to 6 carbons and R.sub.1 is t-butyl, t-pentyl, or cyclohexyl.
Jurd (U.S. Pat. No. 3,973,040) discloses poly-t-butyl-2-cinnamylphenols as mosquito larvae growth inhibitors of the structure ##STR6## wherein n is 2 or 3.